Structure for and method of surface conditioning sensing and indicating and motor speed control

ABSTRACT

The condition of a surface is sensed by cyclically moving two members having engaged surfaces relative to each other, driving the surfaces for only a portion of each cycle to set up a threshold kinetic energy level in accordance with the friction between the engaged surfaces, sensing the kinetic energy developed in one of the members due to moving the members relative to each other, comparing the developed kinetic energy with the threshold kinetic energy and controlling the cyclic movement of the members in accordance with the relationship between the kinetic energy threshold and the developed kinetic energy. The cyclic movement of the members is then used to provide a visual indication of the condition of one of the surfaces.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 957,775,filed Nov. 6, 1978, which is a continuation of application Ser. No.814,000, filed July 8, 1977, which is a continuation of application Ser.No. 565,478, filed Apr. 7, 1975, which is a continuation of applicationSer. No. 340,557, filed Mar. 12, 1973, now U.S. Pat. No. 3,876,919,which is a divisional of application Ser. No. 487,795, filed June 8,1970, now U.S. Pat. No. 3,721,115, which is a continuation ofapplication Ser. No. 666,703, filed Sept. 11, 1967, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to highway safety methods and structures andrefers more specifically to determining the condition of a highwaysurface or the like and providing an indication thereof, particularstructure for providing a signal proportional to the speed of anelectric motor from the motor itself, and a method of and structure formotor speed control with the particular structure.

2. Prior Art

There is considerable emphasis today on highway safety. As a result,automobile manufacturers and highway engineers are attempting to improvethe safety of both automobiles and highways. There are, however, manyparameters of highway safety which are beyond the control of automotiveand highway engineers. One of the significant parameters influencinghighway safety is weather conditions. Weather conditions may produceparticularly dangerous highways due to the degree of slipperiness of theroad surface.

In the past, attempts have been made to determine the condition of aroad surface and to warn approaching motorists when the road surfacecondition is dangerous. Such attempts have often taken the form ofinstruments for measuring the dew point and temperature to determine theexistence of, for example, water or ice on a highway. However, suchdevices have not been the ultimate answer since highway surfaces may beslippery without water or ice thereon. For example, small granules ofsand distributed on the surface of a highway will seriously reduce thecoefficient of friction of the surface so that vehicle tires may slideon the road surface. Therefore, it is desirable to more exactly measurethe coefficient of friction or slipperiness of a road surface ratherthan specific conditions thereof, such as the presence of water or icethereon.

In addition, wherein motor speed control devices have been provided inthe past, they have generally included separate equipment, such astachometers to provide a feedback signal proportional to motor speed.Such additional equipment is expensive and not essential in motor speedcontrol apparatus.

Also, prior speed controls for electric motors have not usually beenfail safe. That is, they have not included structure for preventingoperation of the motor if the motor speed control circuit malfunctions.A fail safe motor control circuit is particularly desirable inconjunction with electrically driven automobiles and the like.

SUMMARY OF THE INVENTION

The invention includes a structure for and method of sensing thecondition of a surface, for example, a highway surface and providing avisual indication of the condition of the surface. A means for and amethod of varying the visual indication of the conditiion of the surfacein accordance with the surface condition is also provided.

The surface condition sensing structure includes an electric motorcircuit in which an additional brush is engaged with the commutatorwhich redistributes the current provided in the armature whereby asignal is available proportional to the speed of the motor which is partof the invention.

The motor speed signal developing circuit of the invention isparticularly useful in providing an efficient, inexpensive method of andcircuit for motor speed control in accordance with the invention. Themotor speed control circuit of the invention includes fail safestructure to prevent operation of a motor controlled by the motor speedcontrol circuit on failure of the motor speed control circuit.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view of structure for surface condition sensing andindicating in accordance with the method of the invention constructed inaccordance with the invention.

FIG. 2 is a top view of the surface condition sensing structureillustrated in FIG. 1 taken in the direction of arrow 2 in FIG. 1.

FIG. 3 is a partial elevation view of the surface condition sensingstructure illustrated in FIG. 1 taken in the direction of arrow 3 inFIG. 1.

FIG. 4 is a schematic diagram of the electrical portion of the structurefor sensing surface conditions illustrated in FIGS. 1 through 3.

FIG. 5 is a schematic diagram of another embodiment of the electricalportion of the structure for sensing surface conditions illustrated inFIGS. 1 through 3.

FIG. 6 is a schematic diagram of structure for providing an electricalsignal proportional to motor speed constructed in accordance with theinvention in a motor speed control circuit for practicing the motorspeed control method of the invention.

FIGS. 7 and 8 are partly schematic, partly block diagrams ofmodifications of the motor speed control circuit illustrated in FIG. 6.

FIG. 9 is a partially schematic, partially block diagram of yet anothermodification of the motor speed control circuit illustrated in FIG. 6,wherein the motor is energized by pulses of electrical energy.

FIG. 10 is a detailed schematic diagram of one embodiment of the motorspeed control circuit illustrated in FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The structure 10 for sensing and indicating a surface conditionillustrated in FIG. 1 includes a disc member 12 of a first materialwhich is the material the surface condition of which it is desired tosense and indicate. For example, the material 12 may be material thesame as a highway surface adjacent which the structure 10 is positioned.The surface of the material 12 and the surface of the highway will thenhave the same coefficient of friction or the same slipperiness under thesame conditions.

The structure 10 further includes the movable member 14 having a surface16 in surface-to-surface engagement with the surface 18 of the disc 12connected to the arm 20 for rotation about the drive shaft 22 extendingfrom transmission 24 which is driven by the motor 26. The resilientmeans 28 is provided between the shaft 22 and the arm 20 for regulatingthe normal force with which the surface 16 engages the surface 18.

As shown best in FIG. 1, the material 12 is mounted at an angle α withrespect to the horizontal and is supported on the frame 30 which encasesthe transmission 24, motor 26 and the electrical portion 32 of thestructure 10. The indicating portion 34 of the structure 10 which, asshown, includes a sign 35 in front of lights 68 may also be enclosed bythe frame 30, as will be understood by those in the art.

A guard 36 of expanded metal is provided, as shown in FIG. 1, to preventplacement of undesirable objects on the disc 12 which would give a falseindication of a surface condition of, for example, a highway adjacentthe structure 10. The diameter of the guard 36 in conjunction with theangle at which disc 12 is positioned with respect to the horizontal andthe angle at which the member 14 is positioned with respect to theradius of the disc 12, together with the extension of the member 14radially beyond the edge of disc 12, will maintain the surface of thedisc 12 substantially clean. Thus, on each revolution of the member 14on the disc 12, the disc 12 will be swept clean. Snow and other solidstending to accumulate thereon will pass between the outer periphery ofthe disc 12 and the guard 36. It is intended that the structure 10 beplaced at a substantial height above the ground adjacent a highway tominimize the chance of tampering therewith and articles being placedthereon and to provide maximum visibility thereof.

The electrical portion 32 of the strcuture 10, shown best in FIG. 4,includes the motor 26 connected between a source of positive electricenergy 36 and ground 38 in series with the emitter collector circuit ofthe transistor 40. A cam 42 is secured to the transmission 24 forrotation at the speed of the motor 26. The cam 42 is mechanicallyconnected to the double throw switch 44. The movable contact 46 of theswitch 44 is connected through a resistor 48 to one side of thecapacitor 50. One fixed contact 52 of the switch 44 is connected toground, while the other fixed contact 54 of the switch 44 is connectedto the source of positive electric energy.

The circuit 32 further includes the potentiometer 58 having a resistor60 in series with a second resistor 62 connected between ground and theother side of the capacitor 50. The wiper arm 64 of potentiometer 53 isconnected directly to ground. A field effect transistor 66 having asource connected through resistor 64 to the source of positive electricenergy and to the base of the transistor 40, a drain connected directlyto ground and a gate connected directly to the junction between theresistor 62 and the other side of the capacitor 50 completes a controlloop in the circuit of the motor 26.

The circuit 32 further includes a plurality of lamps 68 connected inparallel with each other and in series with a source of alternatingelectric energy 70 and a Triac 72. As shown, the control electrode ofthe Triac is connected to the emitter-collector circuit of a transistor74. The emitter-collector circuit of the transistor 74 is connected inseries between the source of positive electric energy and resistor 76.The resistor 76 is also connected to ground. The base of the transistor74 is connected through the resistor 78 to ground and to the drain of asecond field effect transistor 80. The second field effect transistor 80includes a source connected to the source of positive electric energyand a gate connected through a resistor 82 to the gate of the fieldeffect transistor 66 and the junction between the resistor 62 and theother side of the capacitor 50, as shown best in FIG. 4.

In overall operation of the structure 10, it is assumed that the cam 42is out of the θ angle region so that the switch 44 is in the positionillustrated in FIG. 4. Any time that the cam 42 passes through the θangle in its rotation with the motor 26, the movable contact 46 ofswitch 44 will be connected to the positive source of electric energythrough the contact 54. With the switch 44 in the position illustratedin FIG. 4, current will flow from the base of transistor 40 throughfield effect transistor 66 and the resistors 60 and 62 in series toground. The transistor 40 will therefore be on so that the motor 26 willbe driven and the capacitor 50 will be charging to a positive potentialon the right side thereof.

Also, at this time the field effect transistor 80 will be turned on toprovide a voltage on the base of the transistor 74, maintaining thetransistor 74 in an off condition. With transistor 74 off, the Triac 72is actuated by current through resistor 76, whereby the lights 68 areenergized through the power supply 70 by Triac 72.

When the motor 26 rotates into the θ angle, the contact 46 of switch 44engages the contact 54, whereby the positive voltage source is connectedto the left side of the capacitor 50. Then, because the capacitor 50cannot change its charge instantaneously a positive charge on the righthand side of the capacitor 50 equal to twice the positive voltage sourcewill be present. Such charge on the right side of the capacitor 50 willcause the field effect transistors 66 and 80 to turn off.

The turning off of the field effect transistor 66 will turn off thetransistor 40 to stop driving of the motor 26. The turning off of thefield effect transistor 80 will cause conduction of the transistor 74 toplace the gate electrode of the Triac 72 at the positive voltage sourcelevel to turn off the Triac 72 and disconnect the lights 68 from thepower supply 70.

The field effect transistors 66 and 80 remain in the off condition untilthe capacitor 50 can discharge through a time constant, including thecapacitor 50 and the resistances 60, 62 and 48 in series. If prior totiming out of the time constant the motor 26 turns sufficiently to movethe cam 42 through the θ angle, the switch 44 will return to theposition illustrated in FIG. 4 and the capacitor 50 will again start tocharge, the field effect transistors 66 and 80 will turn on and a newcycle of operation of the structure 10 will begin.

In terms of the members 12 and 14, it will be understood that rotationof the motor 26 will rotate the member 14 in surface-to-surfaceengagement with the disc 12 to develop kinetic energy in the member 14.If during rotation of the motor 26, as the cam 24 moves into the θangle, the kinetic energy in the member 14 is sufficient to move themember 14 through the θ angle against the retarding action of thefrictional forces between the surfaces 16 and 18 to start a subsequentdriving cycle of the motor 26 and member 14, the lights 68 will stay onsubstantially constantly. If however, the condition of the surface 16 ofthe disc 12 is such as to provide a high coefficient of friction so thatlittle kinetic energy is developed in the member 14 during rotationthereof and high drag is present on the member 14 in the θ angle, themember 14 will stop in the θ angle some place and a subsequent cycle ofoperation of the structure 10 must await the discharging of thecapacitor 50 through the resistance 62, 60 and 48.

The time constant of the capacitor 50 and of resistances 60, 62 and 48may be considerable, that is, for example, ten minutes. It will,therefore, be understood that the lights 68 of the indicator 34 willilluminate the sign 35 substantially constantly when the surface 18 isof a condition such that the coefficient of friction thereof is so lowthat the member 14 will slide through the θ angle. When the kineticenergy of the member 14 is not equal to the threshold level of kineticenergy determined by the θ angle and the particular materials andstructure 10 so that the member 14 stops within the θ angle during acycle of operation of the structure 10, the lights 68 will be outsubstantially all of the time. That is, for example, with the member 14making one revolution per second and with a time delay or dwell time often minutes, when the member stops in the θ angle, the lights 68 wouldbe on only one six-hundredth of the time. Drivers observing thestructure 10 and particularly the indicator 34 thereof would thus bewarned of a surface condition on the highway matched by the surfacecondition of the disc 12 which provides a dangerously low coefficient offriction between the highway and automobile tires having substantiallythe same material composition as the member 14.

The circuit of FIG. 4 thus provides a slippery or non-slipperyindication to a driver as a warning. It would, however, be desirable ifthe indication were more qualitative. That is to say, it would be ofmore information to a motorist if the length of time the indicator 34were illuminated were related to the degree of slipperiness of the roadsurface. Thus, if the road is slippery enough and the surface 18 is insuch a condition that the member 14 almost slips through the θ angle, itwould be desirable to illuminate the indicator 34 for a longer period oftime than when the surface 18 is not slippery, has a high coefficient offriction and the kinetic energy developed in the member 14 isconsiderably below the threshold value which would allow the member 14to slip through the θ angle. The circuit of FIG. 5 will provide suchoperation of the apparatus 10.

In the circuit of FIG. 5, the motor 26 is a direct current motor,including an armature connected to a commutator and including at leasttwo brushes 82 and 84 engaged with the commutator for passing a directcurrent motor driving signal through the armature of the motor 26. Withsuch a motor 26, a third brush 86 positioned on the commutator willprovide a signal proportional to the speed of the motor 26. In suchstructure, the motor 26 acts in the nature of a tachometer, wherein thesection of the armature between brushes 82 and 86 is rotated in a fixedmagnetic field to provide a signal proportional to the speed of rotationof the armature.

In using a tachometer to develop a signal proportional to motor speedthe voltage developed is purely due to the rotation of the armature.However, when the motor 26 is used to provide a feedback signalrepresentative of the speed of the motor through an additionalcommutator brush 86, the signal at the brush is a function of bothcurrent through the motor and the motor speed. That is to say, that thevoltage across the motor armature is equal to the current through thearmature times the resistance of the armature plus the backelectromotive force in volts per radiance per second times the armatureangular velocity in radiance per second. Thus, when the speed of themotor 26 is low and the current times resistance component is large aspeed control signal based on the voltage across a portion of thearmature is in error. However, with the brush 86 placed close to theground brush 82, the current flowing therebetween is small so that thesignal output from the brush 36 is close to a true function of motorspeed.

The modified circuit 89, illustrated in FIG. 5, includes an additionalbrush on the commutator of motor 26 and the transistor 90 and having anemitter-collector circuit connected between the brush 84 of the motor 26and a positive source of electric energy 92. The base of transistor 90is connected between the resistors 94 and 96 as illustrated. A secondtransistor 98 has its emitter collector circuit connected between theresistor 96 and ground and includes a base connected to one side of acapacitor 100. The base of the transistor 98 is also connected throughthe resistor 102, the resistance 104 and wiper arm 103 to the source ofpositive electrical energy 92 and the other arm of resistor 94 as shown.

The left side of capacitor 100 is connected through a resistance 110 tothe source of positive electric energy and to the movable center contact112 of switch 114. Thus, when the cam 128 driven by motor 26 is outsideof the θ angle, the contact 112 of switch 114 is in engagement with thedead contact 116 of the switch 114 and when the cam 126 is in the oangle, the contact 112 of the switch 114 is in engagement with thegrounded contact 110 of the switch 114.

The circuit of FIG. 5 is completed by the transistor 120 having agrounded collector 120 and an emitter connected directly to the leftside of the capacitor 100. The base of transistor 120 is connectedthrough a resistor 122 and a filter network including a diode 124 and acapacitor 126 to the added brush 86 on the commutator of the motor 26.

In operation of the circuit of FIG. 5, when the motor 26 is rotatingslowly, that is due to a high torque load thereon because of highfriction between the surfaces 18 and 16 of members 12 and 14, a smallfeedback voltage will be fed from the third brush 86 on the commutatorof motor 26 through the diode 124 and resistor 122 across capacitor 126to the base of the transistor 120. The small voltage will not besufficient to turn the transistor 120 on. Therefore, the junctionbetween the resistor 110 and capacitor 100 will rise to the positivepotential of the source of positive electric energy to charge thecapacitor 100 positive on the left side and negative on the right side.The transistor 98 will thus be biased on and the transistor 90 willtherefore also be on to provide driving current through the motor 26.

When the cam 128 is rotated into the θ angle, the contact 112 of theswitch 114 is moved from the dead contact 116 to the grounded contact118. The left side of the capacitor 100 is thus grounded so that adifference in potential of the value of the positive source of electricenergy will appear across the capacitor 100. The transistor 98 is thuscaused to turn off and will turn off the transistor 90 to preventdriving of the motor 26. The time delay will be shorter since thecapacitor is not fully charged.

The transistor 93 will remain in the turned off condition until thecharge on the capacitor 100 has been drained off through the resistancecapacitance time constant provided by the resistors 102, 104 and 110 andthe capacitor 100. This time constant can be changed by the position ofthe potentiometer wiper arm 103. When the transistor 93 is turned on,the lights 68 which may be connected as before to the right hand side ofthe capacitor 100 may be energized through a circuit, such as the bottomcircuit of FIG. 4, to indicate a non-slippery surface by blinking onlyat large intervals.

Assume then that the surface 13 of member 12 is slippery, as when ice orwater have collected thereon to substantially reduce the coefficientfriction between the surfaces 16 and 18 and to increase the keneticenergy in the movable member 14 and the speed of the motor 26, thefeedback voltage from the third brush 36 on the commutator of the motor26 will be sufficient to turn on the transistor 120 so that theresistance offered by the transistor 120 and the resistor 110 will forma voltage divider to divide the voltage of the source of positiveelectric energy. The voltage at the junction between the resistor 110and the left hand side of the capacitor 100 will then be determined bythe feedback voltage from the motor 26 due to the degree of conductionof the transistor 120. That is to say, for example, if the motor 26 isrunning very fast, the transistor 120 will be turned full on and theleft hand side of the capacitor 100 will be substantially at ground.

When the cam 128 passes through the θ angle, the switch 114 again placesthe left hand side of the capacitor 100 at ground through the contact118. The charge on the capacitor 100 will then go from some positivepotential to which it has been allowed to charge with transistor 120 onto ground on the left side during a time constant, again determined bythe resistors 102, 104 and 110 and the capacitor 100. The transistors 98and 90 will again be turned off during this period and the motor 26 willnot be driven and the lights will not be energized.

Now, as the speed of the motor 26 is increased, that is as the surface18 becomes more slippery, the initial charge on the capacitor 100 as thecam goes into the o angle will become smaller and the time that thetransistors 98 and 90 are turned off will become progressively lessuntil the lights 68 are energized substantially all of the time. Thus,the circuit of FIG. 5 will cause the lights 68 to be energized exactlyin accordance with the speed of the motor 26 and the condition of thesurface 18.

As indicated above, the including of an additional brush on thecommutator of motor 23 will provide a signal which is proportional tomotor speed. In FIG. 6 the feedback voltage provided from a third brush142 on an electric motor is used to provide motor speed control.

In the circuit of FIG. 6, the resistors 130 and 132 provide a comparisonbetween the desired speed represented by the position of the wiper arm134 on the resistor 136 of potentiometer 138 with the feedback voltagefrom the motor 140 through the additional brush 142 on the motorcommutator. The feedback signal through the resistor 132 is of a signopposite of the signal through the resistor 130. The difference betweenthese two signals to provide a control signal may be very small if theamplifier 144 has a high gain or in other words is a very large transferfunction. The current through resistors 130 and 132 would in suchstructure be substantially equal when the motor 140 is running at theregulated speed therefor.

When the speed of rotation of the motor 140 is reduced, as for exampleby a heavy load, the feedback signal would be reduced to provide anincreased signal through the amplifier 144 to drive the motor 140 harderand thus increase the speed thereof to bring it back to the regulatedspeed. Similarly, when the motor speed is too high, the error signalprovided the amplifier 144 will be such as to slow the motor down tobring it back to the regulated speed.

The feedback signal from the motor 140 will be a complex signal havingboth an alternating and direct component due to the usual commutatorstructure. If it is desired to operate with only the alternatingfeedback signal, a circuit, such as illustrated in FIG. 7 may be used,wherein a pair of additional brushes 148 and 150 are provided on thecommutator of the motor 146 which brushes are connected to the primarywinding 152 of transformer 154 having the secondary winding 156. Thepurely alternating feedback signal component is then passed through thealternating to direct signal converter to provide operation of the speedcontrol, as in FIG. 6.

Also, as indicated in FIG. 8, by varying the location of a plurality ofauxiliary brushes 158, 160, 162 and 164 on motor 166 different magnitudefeedback signals, each proportional to motor speed, may be tapped fromthe motor 166. These feedback voltages may as indicated be used toenergize auxiliary control units which would then respond to the speedof rotation of the motor 166.

Considering motor speed control through the use of auxiliary brushes onthe commutator of electrical motors further, it will be understood thatthe most efficient way of controlling a direct current motor is withpulses of electrical energy. With such speed controls, transistors arenormally used as switching devices. One such motor speed control 170 isillustrated generally in FIG. 9, wherein the motor 172 is controlled bypulses from the source of power pulses 174 in accordance with thevoltage comparison between the voltage tapped from potentiometer 176 bywiper arm 178 and the electric signal tapped from the motor 172 throughthe brush 180 across the resistors 182 and 183. These pulsed, transistorcontrolled systems are particularly efficient since when the currentthrough the motor is high, the voltage drop across the transistorssupplying the current is small and when the current through the motor issmall, the voltage drop across the controlling transistors is high andthe voltage drop across the motor is small. Consequently the power lossin such systems is limited to a very short time in which the transistoris switching.

In addition, it will be remembered that the motor is basically anintegrator in conjunction with such systems. Consequently the powerpulses for driving the motor 172 are smoothed by the motor. If thefrequency is high enough, it is then difficult to detect that the motoris not drawing power and rotating continuously. Due to this smoothingaction of the motor, the signal generated at the third brush 180 isgoing to be smooth. Consequently, by using pulse width modulation tovary the power to the motor efficiently and by using a third brush toobtain effective tachometer feedback, an efficient well regulated speedcontrol 170 is achieved.

By operating the source of power pulses at as low a frequency asreasonable to obtain smooth operation, power loss in the system isminimized. By operating the source of power pulses or oscillator at neara constant frequency, smooth operation of the speed control is achievedover its operating range. Thus, at start-up, the motor initially turnsslowly and is receiving power pulses at a high pulse per revolutionrate. At high speed, the motor receives power pulses at a low pulse perrevolution rate which enhances the efficiency of the speed control asdescribed above. At high speed, the high momentum of the system allowssmooth operation with power pulses at a low effective pulse rate.

A pulse controlled motor speed control 186 having fail safe features isillustrated in more detail in FIG. 10. In the motor speed controlstructure of FIG. 10, the motor 188 is provided with the usualcommutator brushes 190 and 192 and with the third commutator brush 194for again providing a signal proportional to motor speed. The motor 188is illustrated as having a series field 196 although the indicated speedcontrol could be used equally well with a motor having a permanentmagnet field. The diode 200 is a smoothing diode which provides acurrent with the transistor 202 turned off.

The feedback signal from the motor 188 is again passed through thefilter and current limiting circuit, including the diode 204 andcapacitor 206 and the resistance 208. Again, when the motor 188 isrotated at a sufficient speed, the transistor 210 will be turned on toprovide a current flow through resistor 212 proportional to thefeed-back signal from the motor 188 for comparison with the electricsignal 214 tapped from the resistor 216 of the potentiometer 218 havinga wiper arm 220. The difference in the electrical signals through theresistors 212 and 214 is passed through the high gain transfer circuit222 to again charge the left side of capacitor 224 positive an amountdepending on the speed of the motor 188. It will be noted that thecapacitor is charged while the motor is coasting so that the charge onthe capacitor is more indicative of purely motor speed. That is to say,it is not affected by a power current burst.

The square wave oscilator 226 is provided to return the capacitor 224 toground periodically, causing a voltage change on the right hand side ofthe capacitor 224 sufficient to cause conduction of the field effecttransistor 226 having a gate electrode connected to the right side ofcapacitor 224 and having source and drain electrodes connected to themovable contact of switch 228 and through resistor 230 to the wiper arm232 of potentiometer 234. The field affect transistor 226 will remainturned on for a time determined by the time constant of the capacitor224 and the resistance 236 and the resistor 238 of the potentiometer234. As shown, the wiper arm 232 of the potentiometer 234 is connectedback to the source of positive electric energy 240.

When the field effect transistor 226 is turned on, the transistor 242and transistor 202 connected as shown are turned on to provide currentthrough the transistor 202 and the contacts 228 and 244 of the switch246 to energize the motor 188. The pulse width of the motor energizingpulse through the switch 246 may be regulated by the position of thepotentiometer wiper arm 232 and motor speed control may be effected asbefore.

It will however be noted that in the motor speed control circuit of FIG.10 that a pulse of motor energy is provided during the power pulse whichaccompanies a control pulse, wherein in the motor speed control circuitof FIG. 5 the control pulse kept the power to the motor off. The circuitof FIG. 10 thus has an advantage in the event that the control is usedto drive a vehicle since a loss of control pulses would turn thevehicle's power off. That is the control circuit of FIG. 10 is failsafe. Should the control circuit of FIG. 10 fail by, for example, havingthe field effect transistor 226 or the transistors 242 or 202 short, thealternating current amplifier 248 would no longer receive pulses fromthe transistor 202 through the coupling capacitor 250 and would causethe relay 252 to open the switch 246.

While one embodiment of the present invention and modifications thereofhave been disclosed in detail, it will be understood that otherembodiments and modifications are contemplated by the inventor. It istherefore the intention to include all embodiments and modifications asare defined by the appended claims within the scope of the invention.

What I claim as my invention is:
 1. A motor-signal generator systemcomprising a direct current motor including a commutator and havingthree brushes contacting the commutator, an energy source, a firstelectrically conductive circuit means connected to two of said threebrushes for energizing said motor-signal generator and a secondelectrically conductive circuit means connected to the third and oneother of said three brushes for deriving a signal generated within themotor-signal generator when the motor is rotationally displaced, saidsignal having an alternating current component, said second electricallyconductive circuit means including means for obtaining the alternatingcurrent component of said signal.
 2. In a motor system for driving anoutput intermittently in complete steps, comprising a direct currentmotor including a commutator and having three brushes contacting thecommutator, a source of energy, a first electrically conductive circuitmeans connected to two of three brushes for de-energizing said motorautomatically near the end of each step for a dwell period andautomatically energizing said motor after said dwell period to start thenext step, capacitive timing means to determine said dwell period, motordriven switch means operably associated with said first electricallyconductive circuit means so energy is provided to said motor wheneversaid output is within a step and energy is not provided to the motorduring a dwell period, a second electrically conductive circuit meansconnected to the third and one other of the said three brushes forderiving a signal generated within the motor operably associated tocondition the capacitor such that when the signal is larger, the dwelltime is shorter.
 3. A motor system for driving an output intermittentlyin complete steps, comprising a direct current motor including acommutator and having three brushes contacting the commutator, a currentsource, a first electrically conductive circuit means connected to twoof three brushes for de-energizing said motor sutomatically near the endof each step for a dwell period, capacitive timing means to determinesaid dwell period, motor driven switch means operably associated withsaid current source so the current flow is synchronized with theposition of said output, supplying current to the motor when the outputis within a step and stopping the flow of current to the motor for saiddwell period, a second electrically conductive circuit means connectedto the third and one other of said three brushes for deriving a signalgenerated within the motor and used to condition said capacitor suchthat when a step is traversed in less time, the dwell time is less. 4.In a motor system as described in claim 2, wherein the motor drivenswitch means is at ground potential during a dwell period.
 5. In a motorsystem as described in claim 2, wherein the dwell time is reduced tozero when the signal generated exceeds a predetermined value.
 6. Amotor-signal generator system comprising a direct current motorincluding a commutator and having three brushes contacting thecommutator, an energy source, a first electrically conductive circuitmeans connected to two of said three brushes for energizing saidmotor-signal generator, a second electrically conductive circuit meansconnected to the third and one other of said three brushes for derivinga signal generated within the motor-signal generator when the motor isrotationally displaced, said system including pulse width modulationmeans whereby said signal generated within the direct current motormodulates the time interval of the energizing of the motor.
 7. Thesystem of claim 6, wherein as the signal generated in the direct currentmotor becomes larger in magnitude as the time interval during which themotor is de-energized becomes larger.
 8. A motor-signal generator systemcomprising a direct current motor including a commutator and having fourbrushes contacting the commutator, an energy source, a firstelectrically conductive circuit means connected to two of said fourbrushes for energizing said motor-signal generator, and a transformerprimary forming a second electrically conductive circuit with the othertwo brushes for deriving in the secondary of said transformer analternating component of a signal generated within the motor-signalgenerator when said motor-signal generator is rotationally displaced. 9.The system of claim 8 and further including an alternating current todirect current converter in circuit with the secondard of saidtransformer to provide a direct current signal proportional to thealternating current component of the signal generated within themotor-signal generator.
 10. A motor-signal generator system comprising adirect current motor including a commutator and having three brushescontacting the commutator, an energy source, a first electricallyconductive circuit means connected to two of said three brushes forenergizing said motor-signal generator, a second electrically conductivecircuit means connected to the third and one other of said three brushesfor deriving a signal generated within the motor-signal generator whenthe motor is rotationally displaced, and capacitor means forconditioning the derived signal to control an operation in response tothe rate of rotation of the motor.
 11. The system of claim 10, whereinthe operation controlled is the rate of rotation of the motor.
 12. Amotor-signal generator system comprising a direct current motorincluding a commutator and having three brushes contacting thecommutator, an energy source, a first electrically conductive circuitmeans connected to two of said three brushes for energizing saidmotor-signal generator, a second electrically conductive circuit meansconnected to the third and one other of said three brushes for derivinga signal generated within the motor-signal generator when the motor isrotationally displaced, reference signal means, comparator meanscomparing the signal generated within the direct current motor with theoutput of said reference signal means to form a comparator output, andamplifying means amplifying the comparator output and modulating theenergization of the motor with the amplified comparator output.